This invention relates to a solid state imaging device, and more particularly to a solid state imaging device used in an improved assembling structure for a subminiature electronic camera and an electronic endoscope or the like.
Recently, the electronic endoscope and the micro-camera, etc., have been developed as applied products using the solid state imaging device A fine tip portion for the endoscope to be inserted into a human body, and a small size for the camera-head of the micro-camera are important salespoints with these products. Therefore, it is desirable for the solid state imaging device assembled therein to be as small as possible. This solid state imaging device is composed of peripheral circuit components, including a noise reduction circuit or an amplification circuit, etc., and extension cables. The external diameter of the tip portion of the electronic endoscope has a direct influence upon the size of the solid state imaging device. As a result there has been an effort to miniatuarize the size of the solid state imaging device.
An example of a typical conventional solid state imaging device assembled in an electronic endoscope is shown in FIG. 11. A solid state imaging element 61 is disposed on a flexible printed circuit board (FPC) 62. Peripheral circuits constructed by chip components 63 are assembled adjacent to the solid state imaging element 61 on the FPC 62. The solid state imaging element and a picture signal processing circuit are connected using and an extension cable of one or more meters. Therefore, minimum necessary peripheral circuits, such as a noise reduction circuit, and a picture amplification circuit etc., must be disposed close to the solid state imaging element 61. In the electronic endoscope, an observation system including lenses to focus the image on the solid state imaging element and in addition, a light guide for a lighting system and a treating channel must be accommodated usually into a flexible tube. Further, the flexible tube must be fine size.
The solid state imaging element 61 is composed of chip carriers 70 made of ceramic, a CCD (charge coupled device) element 66 and a light transparent cover 67 made of optical glass. A cavity 68 is provided on the chip carrier 70. Connection patterns (not shown) are provided surrounding the cavity 68 of the chip carrier 70. The CCD element 66 is disposed in the cavity 68. Electrodes (not shown) of the CCD element 66 and the connection patterns (not shown) of the chip carrier 70 are bonded using fine metal wires 69. Thus, the solid state imaging element 61 and the FPC 62 are connected electrically and mechanically through the chip carrier 70.
As above-mentioned, a pad portion and an adhesion portion for the light transparent cover 67, etc., are indispensable to the chip carrier 70 composed of the solid state imaging element 61, and these portions determine the overall size of the device. Namely, the overall construction of the device has a large size, so that the size of the chip carrier 70 has to be larger than the size of the CCD element 66.
In the construction shown in FIG. 11, a prism 64 is disposed on the solid state imaging element 61 to define the diameter of the flexible tube, and the light receiving plane 71 of the CCD element 66 to receive the imaging light 65 is disposed at 90 degrees to the object being observed. However, the light receiving plane of the CCD element has been oriented directly toward the object. In this case, the prism is unnecessary, but the outer size of the device is determined by the size of the chip carrier, because the solid state imaging element has to be oriented vertically in the configuration of FIG. 11. Furthermore, it was necessary to bend the FPC assembled peripheral circuit components thereon 90 degrees, and to provide the FPC on the back side of the chip carrier 70. As a result, instances of deterioration of the FPC and damage or cutting of the wiring layers on the FPC were increased.
The miniaturization of the solid state imaging element itself has been advanced. As a result, the volume of the peripheral circuit components occupied in the solid state imaging device also has increased. Therefore, the width of the FPC becomes narrow as the size of the solid state imaging element decreases. The length of the FPC must be increased to assemble the peripheral components thereon.